The invention relates to a display device comprising an electro-optical display medium between two supporting plates, a system of pixels arranged in rows and columns, with each pixel being formed by picture electrodes arranged on the facing surfaces of the supporting plates, and a system of row and column electrodes for driving the pixels, a picture electrode on one of the supporting plates being connected in an electrically conducting manner to a first switching unit between a column electrode and the picture electrode and to a second switching unit between an electrode for a reference voltage and the picture electrode.
A switching unit may comprise one or more switching elements such as diodes or MIM's.
A display device of this type is suitable for displaying video information and also, for example, alpha-numerical information by means of passive display media such as liquid crystals, electrophoretic suspensions, electrochromic materials, etc.
The invention also relates to a supporting plate for use in such a display device.
A display device of the type described in the opening paragraph is known from European Patent Application No. 0 299 546 (PHN 12.154) corresponding to U.S. Pat. No. 5,032,831. In a device described in this Application the pixels are given a specific adjustment per row by accurately charging or discharging the capacitances associated with these pixels after first having discharged or charged them too far. Prior to selection an auxiliary voltage beyond or on the limit of the voltage range to be used for picture display is applied across the pixels. In one of the examples this is effected by means of switching units comprising diodes which are connected to a suitably chosen reference voltage.
A problem which occurs in the manufacture of such a display device is the possibility of tests on the active supporting plate carrying picture electrodes and the non-linear switching elements (diodes). This problem is caused because all picture electrodes and their associated switching elements are arranged parallel, as it were, in one column between the relevant column electrode and an electrode for a reference voltage. Separate measurement of the picture electrodes and their associated switching elements is thus not possible.
If a display device of the type described in the opening paragraph is to be used for colour display, it is preferably provided with a colour filter in which the colours (for example, the primary colours red, green and blue) are arranged in accordance with a "delta structure". This means that two rows of pixels are consecutively driven for one row of complete pixels (each comprising three composite pixels).
To inhibit degradation of the liquid crystal material, the pixels are regularly driven with opposite polarities, for example, every subsequent frame period. To inhibit "large-area flicker", the polarity is also reversed within one frame period after every two rows of pixels have been driven ("double-row inversion"). However, this may give rise to a slightly striped image. Another drawback is that a column electrode must be provided alternately with signals of different colours, which makes the drive electronics additionally complicated.
A further drawback of the known display device is that voltage lines for the reference voltage are provided between the pixels in the column direction. In this case one electrode usually alternates with two electrodes, between the columns of pixels, viz one electrode for the reference voltage, two column electrodes, and so forth. Such a division is not only at the expense of the effective image surface area but also gives rise to artefacts in the image.